Shift in the wavelength of peak sensitivity of the cone photo pigments
is a major cause of inter-individual variations in the Rayleigh match.
Normal color observers performed multiple Rayleigh matches (i.e., a series
of seven Rayleigh-type color matches using various sets of test and
primary lights) in order to derive estimates of the M- and L-photo pigment
wavelengths of maximum absorbance. We predicted the ratio of incident
radiances Pr/Pg for a range of
plausible values in terms of wavelength of the peak sensitivity of the
M-cone and L-cone. An algorithm allowed us to adjust the values of the
peak wavelength of the cone photo pigments in order to minimize the sum of
squared differences between predicted and real results of matches. To
create candidate M-cone and L-cone photo pigments that best predict the
set of equation values, we used the low density spectral absorbance curves
of the M-cone and L-cone photo pigments respectively, as tabulated by
Stockman and Sharpe (2000), and shifted each
template along a logarithmic wavelength scale. For all observers, the
system of seven Rayleigh-like equations converges to a unique solution. M-
and L-cone photo pigments are estimated separately. The distribution of
the wavelength of maximum sensitivity of the photo pigments includes a
cluster. Only a few women's results lie outside the cluster. The
choice of the template has a considerable influence on the convergence of
the algorithm.